The two main causes of the battery light coming on are the alternator failing, and the ignition switch failing. Do the dash lights light up at key on?
The battery light will come on with a bad ign switch because the alternator controls the light, and gets a ignition switched power feed from the fuse box to let it know at what voltage it is charging. So with high resistance through the switch, the ignition circuits of the fuse box may only be seeing 10v, even with the alternator putting out 14v to the battery. This 10v is seen by the alternator as inadicute charging, and the alternator will ground it's feed to the I/P through the ECM.
Try starting it a few times over the course of the next little while, it will start eventually...
After I wrote this much, I feel the need to ask, what year? The above information is based on an 03-05 with the BMW engine.
But once you get it running, check the voltage at the battery, then at fuse 1 in the interior fuse box behind the glove box. If there is a significant difference, you're most likely looking at a bad ignition switch.
If none of this applies due to model year, then there is a chance that you may have a wiring issue, or a failing battery with a, or multiple bad cells.
I have something similar, my ignition switch will not turn unless I first disconnect/ reconnect the battery!! You think it's a bad switch and needs replacing? I did a search and other people had the same problem.
No, the switch itself has very little to do with the key turning.
The key being able to turn is based on a lock out solenoid built into the switch, controlled by the Immobilization ECU and the Steering Column Lock ECU. I haven't seen one that would only work after a battery disconnect, but usually when the key won't turn, it is due to a bad steering column lock ECU. The best way to know this for sure, is to have the Steering Lock History pulled from the vehicle, and you will see many errors when it is bad. The 2 other symptoms that I have seen along with the key not turning are,
Steering wheel unlocked (so that you can turn the wheel with the key off, obviously without the engine running it is a work out to turn, but it should be locked and only move a couple of inches)
The steering column making a ratcheting sound when the key is inserted or removed from the ignition, kind of like a repeated series of the normal clicks it makes
The ignition lock solenoid has two different strategies, it is unlocked when a valid key is inserted (once the ring picks up the chip in the key) and it is also preemptively unlocked for a minute when the vehicle receives an unlock signal from the remote. Both of these are controlled by a combination of the two ECUs mentioned above, and will be disabled if the steering column does not report that it has successfully unlocked.
It is usually a simple and quick diagnosis, with the right equipment, and the steering column is easy to replace, book time is 1.6 hrs. I would assume they could get it done in a day, unless they had to order the part.
The steering column is not special order in the way that a key is, but that is not to say your dealership will have it in stock. But they will be able to get it the next day, probably with a delivery charge to you.
Well I went to a local dealer here in So.Fla. to inquire about the s.column. Guess what?? They said that it was in fact the S.C. Ecu. The price for a brand new column, which by the way is on backorder, cost, if I was fool enough to buy it, a whooping $7,460 American dollars!!!!!!!! This price was for the part alone, installing it was not quoted to me, but I think it calls for 1.6 to 2.0 hrs. labor. What I did is this. After I left the dealer, took a cold shower to get me out of the shock!!! I said to myself, Self... There has to be an easy way to use a toggle switch to stop the current flow through fuse #18, that's what I did!!! I bought two small fuse taps, found a blown fuse and used one of the taps on either fuse contacts and installed an in-line toggle switch with a wire long enough to reach the center console. Now when I need to start the truck I flip the switch off and on Wait approx. 30seconds and I'm good to go. By flipping the switch it interrupts the current through fuse #18 and resets the ECU in the column. This way you don't have to take the fuse out every time. It works for me!! Cheers!!!
I don't know why they quoted you the price for a new one, there is a reman available(last time I checked it was in stock in the warehouse, but it's been over a month) but I believe it was around $1200 or so then.
I did just a quick google search, and it seems like the aftermarket suppliers(that sell OEM parts, such as Atlantic British) do not have any in stock. There may be a shortage of them, and no longer any reman units available. It has been a little while since I replaced one, and sometimes parts inventory can change overnight. If nothing else, I would give a dealership a call, and get price and availability of the part number above. Good luck.
I put the tabs in and wired it all up - works great.
My question is, "What's the best way to utilize this?" Currently, after I turn the truck off I remove the key, flip the switch off/on and then lock it up. When I return I start the truck and leave the switch on. However, I wonder if this is wise since I did not put an inline 10a fuse. Since it was 10a, I assume when the switch is on there's quite a bit of power running through the system. I don't know why this would be the case because if I turn it off once I have it started the truck runs just fine. One thought I had was to just turn it off immediately after the truck starts, then turn it on after I remove the key.